FUNCTIONS AND STRUCTURES OF THE MOTOR CORTICES IN HUMANS

Humans and non-human primates have several motor areas. Exactly how ma ny is a matter of current debate. A proper parcellation of motor areas must be based on correlated structural and functional differences. Re cent studies indicate that the primary motor cortex may be, in reality , two areas (46 and 4p). Similarly, there are undoubtedly two or more cingulate motor areas and perhaps two supplementary motor areas. The h omologies between human and monkey brains are striking in some cases, making monkey models of human motor cortices attractive. The doctrine of a strict 'homuncular' somatotopical organization of motor areas wil l have to be abandoned. The engagement of motor areas in different typ es of voluntary seems merely a matter of degree of activation rather t han exclusive specific contributions.